The purpose of the present research is to identify and describe the effects of psychomotor stimulants, barbiturates, opiates and opiate antagonists on selected physiological systems in conscious nonhuman primates. Squirrel monkeys and baboons will be surgically prepared with chronically indwelling arterial and venous catheters for the direct measurement of blood pressure and intravenous administration of drugs. A wide range of doses of each drug will be administered acutely to determine the effects on systemic arterial blood pressure, heart rate and temperature. In other monkeys, the same drugs will be administered chronically to study the effects of chronic administration and, subsequently, termination of chronic administration on arterial blood pressure, heart rate and temperature. Experiments in baboons will study changes in blood chemistry, blood pressure and heart rate due to chronic administration of the drugs, and due to the administration of drugs in combination. Other experiments in squirrel monkeys will study changes in physiological activity during ongoing behavior maintained by drug injection, food presentation or the postponement of electric shock and the effects of psychomotor stimulants, barbiturates, opiates and opiate antagonists in altering the behavioral and physiological activity. The research will provide definitive information on the way these classes of drugs affect blood pressure, blood chemistry, heart rate, temperature and behavior, and the extent to which the effects can be blocked or antagonized.